1. Field of the Invention.
The present invention relates test specimen loading machines that substantially reduce unwanted lateral loads being applied to the specimen while using servo-mechanical loading drives.
2. Description of the Prior Art.
Various screw-driven actuator tension compression test devices have been advanced in the prior art, such as an electro-mechanical actuator for a test frame made by the Instron Corporation, which has a motor mounted below a test frame cross member, and a non-rotating ball screw driven by a rotating nut. A high speed motor is used to drive a gear box through a belt drive and the output of the gear box rotates the nut to load a specimen coupled to the ball screw through a specimen grip. The mounting for the motor requires the use of a torque arm for preventing the motor from rotating when the motor is driving the nut and screw.
Additionally, the Schenck Corporation sells a test frame which utilizes a screw driven actuator with a motor that is mounted below a main base on the test frame, and which uses a frame that is guided on the columns for the test machine to attempt to eliminate side loading of the specimen.
The above described devices require substantial reductions in motor speed using transmissions, and the Schenck device does not provide internal support for the movable loading shaft so that external guiding is required or else side loads on the specimen are present.
A number of patents have also issued for screw actuated test machines, and in particular there are a number of patents which show screws which move and load the main outer columns of test machines. A typical device is shown in U.S. Pat. No. 3,859,848. This test frame utilizes ball screw members for moving a crosshead. The ball screw members form the side support columns.
A ball bearing vertical shaft guide is shown in U.S. Pat. No. 3,357,755, which provides for vertical movement of a shaft as guided by a plurality of balls in an outer housing or race. This guide is for a die-set, and provides a stablized axial guide.
U.S. Pat. No. 3,375,709 shows a loading device which has screw actuated crossheads with edge guides.
U.S. Pat. No. 3,859,848 shows screw actuated crossheads as well with independent supports shown for the loading device for the grips.
U.S. Pat. No. 4,096,741 shows a central load member which is run with a linear motor rather than a screw actuator. A screw is used for taking up slack and providing stop members for a slider.
A sliding spline assembly that slides in a ball bearing housing, which is of the type used for guiding a movable shaft in the present device, is shown in U.S. Pat. No. 4,620,351. The ball-shaft slide assembly that is used for stablizing the loading shaft in the present test machine arrangement is commercially available.
A similar device that provides for nonrotation guiding of a shaft inside a ball housing assembly is shown in U.S. Pat. No. 4,705,491.
U.S. Pat. No. 3,203,232 shows a testing machine with screws at the outer edges of the crosshead used to move the crosshead. This type of mechanical loading device shows ball screws for driving the loading members.